The disclosure relates to a communication network where data are provided by devices and in which nodes exchange data via wired link. The disclosure may be implemented in a communication network for seismic data acquisition systems in which nodes are connected with seismic sensors. In this application, seismic sensors disposed on the Earth's surface receive seismic wave trains resulting from emission into the ground by a seismic source. Treatment of these reflections can build a map of the subsoil prospected. The present disclosure is usable for the oil exploration industry using seismic methods.
However, the disclosure is not limited to the particular field of oil exploration industry and may be used in any data acquisition system in which data acquired by each node in the network is transmitted and received by other nodes using wired links.
In the case of data acquisition systems comprising seismic sensors, these devices are connected together in strings by cables to an electronic unit named a “node”. These nodes are usually placed in lines and managed by devices, also referred to as “concentrators”. A set of a plurality of nodes surrounded by concentrators at each end is called a “segment”. A node may also end the segment. Each concentrator locally manages communication on a segment, and provides the power supply to the nodes. Concentrators communicate with a central unit that controls all devices and centralizes the data transmitted over the communication network.
When the devices are placed and connected, they are turned off. The activation of each unit is performed by successively turning on the power supply according to the propagation of electric voltage. Following its powering on, the device is activated and sends back a signal to the device that provided its power supply, i.e. the previous device, this signal being iteratively propagated towards the beginning of the segment. The concentrator placed at the beginning of the segment receives the frame corresponding to each node switching on and may thus count the number of nodes connected to this segment. If an identifier of each node is transmitted, the concentrator may also identify each node in its segment. The concentrator then sends a new activation signal and a new device is switched on. These operations are repeated until the end of the segment is found or another concentrator is reached. To turn on the entire network, each node is individually switched on and then; data can get over this node and reach the rest of the segment. The above procedure results in a time consuming initialization phase for turning on the network.
A super frame is defined as the appending of a control frame, successive data frames and an end of super frame symbol, with a size of super-frame fixed to the maximum node count specified for the system.
Document EP 1087240 discloses a seismic data acquisition system according to the prior art. As also disclosed in EP 1087240, such a network may comprise many concentrators connected to a greater number of nodes. At any time, operators may disconnect some cables to install new nodes or concentrators: the network topography may often change. Moreover, the cables may be partially or completely cut due to environmental stresses, thus isolating some portions of some segments. To overcome this problem, it has been proposed to implement the data acquisition system in main acquisition line (comprising the segments) interconnected by secondary transverse line also connected to the central unit. The use of main and secondary transverse line builds loops and allows multiple paths to transmit the data. Thus, loops topography may avoid lines cut transmission issues. The events affecting the topography network may frequently occur, therefore it is necessary to have a network whose topography is dynamically managed and that is able at any time to detect cuts and transmit data by other paths. In some regions, after a night of inactivity, rodents may damage the network (cable or device). The duration to restart the network system may take a long time, sometimes several hours. This time is very expensive for operators.